There is a need for microspheres with properties that are advantageous for many types of applications, including medical applications. Microspheres with high density, yet a large capacity to swell in an aqueous environment, would be useful for absorption applications such as small-scale spill control and for delivery applications in which they would carry and release active ingredients such as fertilizers, herbicides, pesticides, cosmetics, shampoos, and medications. Microspheres with additional properties of durability and deformability would provide a valuable material for introduction into animals, including humans, for applications such as tissue augmentation, void filling, wound treatment, and embolization. Tissue augmentation involves introduction of materials in a collapsed area to provide a filling function, such as the treatment of scars or wrinkles. Void filling involves introduction of materials into an empty space, such as one created by removal of a tissue mass. Wound treatment involves introduction of materials to stop bleeding, provide padding, deliver medication, and absorb fluids. Such materials are useful especially in emergency situations including accidents and military operations. Embolization treatment involves the introduction of a material into the vasculature in order to block the blood flow in a particular region, and may be used to treat non-cancerous tumors, such as uterine fibroids, and cancerous tumors, as well as to control bleeding caused by conditions such as stomach ulcers, aneurysms, and injury. Blockage may be desired in the case of arteriovenous malformation (AVM), where abnormal connections occur between arteries and veins. Additionally, blockage may be desired for pre-surgical control of blood flow.
Hydrogel microspheres have been produced and used in tissue augmentation and embolization treatments. Properties of a sample of microspheres are generally related not only to the materials used in microsphere preparation, but also to the process by which the microspheres are prepared. U.S. Pat. No. 6,218,440 discloses a process for preparing hydrogel microspheres in which an emulsion is first prepared, and then this emulsion is suspended in an oil medium. Microspheres formed by this process have many cavities joined by interconnecting pores, with cavities at the interior of the material in communication with the surface, since a porous crosslinked hydrophilic polymeric material is produced.
U.S. Pat. No. 4,446,261 discloses a process for making hydrogel microspheres which includes dispersing a solution containing monomer, crosslinking agent and initiator in a dispersion medium consisting of hydrocarbons having from 6 to 10 carbon atoms or halogenated aromatic hydrocarbons, with a protective colloid dissolved in this oil material.
U.S. Pat. No. 6,436,424 discloses microspheres suitable for dermal augmentation that are said to swell upon contacting physiological fluids at the injection site to up to four times the average diameter of the microspheres prior to injection. These hydrogel microspheres are said to be made by standard methods of polymerization and microsphere preparation described in the art. The microspheres described in U.S. Pat. No. 6,790,456 are the same as those described in U.S. Pat. No. 6,436,424.
JP1994056676A discloses a suspension used for embolization containing lipidic contrast agent and highly water absorbent hydrogel particles of vinyl alcohol and sodium acrylate polymer that are approximately 1.0 mm in diameter or less.
There remains a need for a new process to prepare microspheres which is simple, consistent, and produces microspheres with valuable properties.